We have only identified a fraction of the bacteria that are normally present inside of us and there is still a lot to learn. What researchers are confident about though is that including foods that promote a variety of healthy bacteria to grow in our gut should be included in our diets.
So what kind of foods does this include?
Well the most common would be things like yogurt, sauerkraut and sour cream. Less common ones you may want to try include kefir (a fermented milk drink), kombucha tea and kimchi (pickled cabbage).
There are lots more out there so be sure to try out a bunch to see what is right for you. These products are naturally fermented and have the good bacteria we need. There are 'probiotic' products on the market which have extra bacteria added to them. Unless you have been on an antibiotic or have had a medical procedure that would have killed off a lot of the bacteria in your stomach (like stomach surgery), you will get just as much benefit from the regular product so don't worry about dropping the extra cash.
However, it is important to point out that those that have had long term stomach issues may benefit from taking a probiotic supplement. Be sure to speak to your doctor or dietitian first to find out which one is right for you.
It is important to be cautious with fermented foods since many are high in salt or sugar which are commonly used in the fermenting process. If you have to limit either of these things, be sure to mind your portions and read the labels.